Cranky Camaro - HOT ROD to the Rescue

If your hot rod has a gremlin that just won’t quit, you could be one of the lucky candidates chosen for a hands-on thrash. Drop us a line at pitstop@hotrod.com, and put “Rescue” in the subject line. We won’t repair factory stockers or build you a whole car, but HOT ROD and industry experts will fix the immediate problem.

The Combo

For the Trujillos, it was love at first sight and a rekindling of their high school car hobby when they spotted and managed to snag this classic ’69 Camaro SS equipped with a hopped-up 350 small-block, a TH350 automatic trans with a 10-inch converter (2,800-rpm flash), and a 3.31:1-geared 12-bolt rearend with an open diff. The short-block’s origins, internals, compression ratio, and healthy flat-tappet hydraulic cam’s exact specs are unknown, but it is topped by Chevy Phase 2 Bow-Tie iron heads and runs best on premium gas. External bolt-ons include a Holley Street Avenger 670-cfm vacuum-secondary carb, a Weiand Team G single-plane intake, Doug’s tri-Y headers, and an MSD distributor controlled by an MSD 6A box.

1/17Owners Gilbert and Laura Trujillo, post-fix: "I was thrilled with how the tuning turned out," Laura says. "It's almost like a brand-new car."

The Problem

It may have been love, but all relationships go through their rocky patches. “The car was previously known for running very rich,” Gilbert says. “It had been nearly 20 years since I worked on cars, but we tinkered with it and got it to run a little better. The timing was way off, and the fast idle speed was adjusted way too high to compensate for the lack of timing. But it still has a problem or two, especially when it gets up in temperature.”

“A problem or two” is stating it mildly. Although there were no overwhelming deal-breakers, the Trujillos reported a variety of ongoing driveability glitches: hard starting and “flooding out,” most noticeably in the summer, after the car sat and heat-soaked for an hour; problems at cold start in the morning (“the car will usually start if I hold the throttle to the floor”); a Third-gear surge at part-throttle, steady-state cruise; and occasional detonation “when the engine temperature rises.”

To scientifically diagnose and resolve the problem, we set up a chassis-dyno evaluation for the Bellflower, California–based car at one of our favorite SoCal test-and-tune facilities, Westech Performance in Mira Loma. Ace Westech tuner Ernie Mena let the car sit overnight so he could deal with the cold-start problem.

The Fix: Driveability

Next morning, the car wouldn’t start cold and idle properly. The primary and secondary float levels were correct, and the electric choke was correctly hooked to a full-time, hot-in-crank-and-run, 12-volt power source, yet dead cold, the choke blade was fully closed. Mena got the car to start by adjusting the over-rich choke setting slightly leaner. That got the car to start up, but after initial cold fire-up, it idled erratically lean. Richening the idle mixture screws (turning them counterclockwise) stabilized the idle, enabling Mena to make an initial dyno run.

During the first run, there was an occasional audible “click,” as if something was grounding out. Sure enough, one spark-plug wire was burned through against a header pipe. It turned out to be the root cause of the erratic idle, and replacing the wire went a long way to smoothing everything out. See how you can end up chasing your tail?

Mena was then able to dial in the proper idle quality by leaning out the idle mixture screws (turning them in) until the engine changed tone, then backing them out about ¼-turn, and finally fine-tuning the idle speed by turning the curb idle adjustment screw almost all the way out to get the idle under control with the big cam. The final hot-idle speed ended up at 825 rpm (before it wouldn’t idle below 1,000). Getting the idle mixture right and the curb-idle speed under control also solved Trujillo’s hot-soak flooding complaint. The occasional surge at part-throttle cruise was caused by a lean primary circuit, easily fixed with slightly richer primary jets.

The Fix: Ignition Curve

Next, the Camaro’s full-throttle performance was evaluated. At the balancer, the timing appeared to be set at 14 degrees initial, advancing to 46 degrees total at 3,500 rpm, and still climbing—just like a typical lazy stocker. After popping the distributor cap, it was apparent that someone previously tried to speed up the curve with two lightweight silver springs and a thin bushing. The usual procedure is to add a thicker distributor bushing to limit total advance, increase initial timing, and add softer springs to make the advance come in quicker. On this car, Mena achieved the desired advance rate with a thick bushing, one light silver spring, and one medium-tension blue spring. Getting the bushing to fit took some work; the distributor was a very early MSD unit that didn’t accept standard-configuration bushings. The advance was reset to what appeared to be 23 degrees initial and 40 degrees total. But the car still felt sluggish on the dyno.

Mena had a feeling the timing pointer wasn’t accurately indicating true top dead center (TDC). He turned over the engine by hand and looked into the No. 1 cylinder with a borescope as the piston rose up in the bore. Sure enough, the zero mark was actually 10 degrees retarded! The reason for that is unknown, though it could be a mis-indexed crank key, the wrong balancer for the application, the wrong front cover (it had a weld-on tab), or a combination of these factors. After accurately re-marking the tab, the engine responded with 24 degrees initial and 42 degrees total, all in by 3,200 rpm. That seems like a heck of a lot of timing, but Mena said it’s typical for an old, low-compression small-block with “lazy” combustion chambers.

The Fix: WOT Fuel

Although initially lean on the primary side, at an 11.9–12.1:1 wide-open-throttle (WOT) air/fuel (A/F) ratio, the car was too rich at wide-open for Mena’s taste. Yet the secondary jets were only No. 72s, seemingly within reason. Maybe the vacuum-secondaries weren’t fully opening? Nope, they were opening fully with no hesitation using the original, as-delivered, plain-colored, secondary spring. Throttle linkage too short? OK as well. So Mena tried No. 68 secondary jets, which leaned the WOT A/F ratio to 12.3 to 12.5:1. That’s better but still not as lean as you’d expect from a four-number jet change. And engine output remained the same as before. Mena says, “I didn’t want to keep pulling jets out compared with the now-richer primary side. As a street carb, there’s no secondary air-bleed adjustments, so it’s about as good as you’re going to get and still stay safe for daily street driving.”

Results

The car now starts properly both hot and cold. Idle vacuum is higher (about 13 to 13.4 in-hg versus 11.5 initially), and there’s no dieseling (run-on) after shutdown. Trujillo says after hot soak “the car fires right up without touching the gas. There’s no more flooding, everything’s correct.” When you get on it, that one-legger rearend really lights up the tires. (Posi, anyone?) The only remaining glitch (and it’s just barely noticeable) is a slight flat spot; creeping along about 20 mph, there’s a slight pause where the rpm doesn’t immediately increase when you slowly step into the throttle. Mena says it’s “primarily a weak signal because of the single-plane intake’s large plenum volume. Changing to a high-rise dual-plane would provide a stronger signal at low rpm, especially as this engine doesn’t make power over 5,600 rpm.”

Lessons Learned

There’s a complex interaction between the carburetor, ignition curve, and various small defects that can gang up to cause mysterious driveability ills. Check the basics first before trying to cover up the underlying problem by gross timing, choke, and mixture adjustments.

17/17On Westech's SuperFlow chassis dyno, at the wheels Trujillo's Camaro baselined at a corrected 295 lb-ft of torque at 3,900 rpm, with 265 hp on tap at 5,600. It left with 317 lb-ft at 3,100 rpm and 288 hp at 5,650, a gain of 22 lb-ft and 23 hp. The overall curves were also broadened over the baseline; the torque-curve dip between 2,850 and 2,950 was eliminated.